A group of 20 high school students partake in an elite class to prepare for a college exam. Among them are the rebellious Kang I-na, her best friend Yoon Myong-heo, and the class clown Kang Hyun, who harbors an affection for I-na. After several strange incidents, the class is interrupted by a TV showing of the top-ranking student, Min Hye-yeong, being trapped in a glass being slowly filled with water. A voice over the PA system announces that questions will be posed to the class; failure to answer them in time will lead to their death. It also warns them and their two teachers, Hwang Chang-wook and Choi So-yeong, against leaving the school. The class fails to solve the first question to save Hye-yeong.
Despite the warning, the class tries to leave, only to find that a teacher and hall monitor, Mr. Lee, was beaten to death, leaving only Mr. Kim to guard them. The students split up and try to answer the questions while also attempting to find a way out. Several students die, then Beom, who earlier tries to strangle I-na and was put in a mental facility, escapes and attempts to kill I-na, but Hyun shields her from the attack and dies. Chang-wook then kills Beom. I-na discovers to her horror that Myong-heo has also been kidnapped by a mysterious woman. They fail to save her and Chang-wook strangles the woman to death.
A memorial is held for the students killed, then I-na is kidnapped unnoticed. One final question is posed: have the person who killed his daughter step forward and confess. The person in question, a now-demented Chang-wook, reveals himself and is killed by the mastermind, who turns out to be Mr. Kim. I-na is then freed by So-yeong.
Flashbacks reveal that Kim's daughter, Kim Ji-won, worked hard to enter the elite class. However, the parents of the killed students bribed Chang-wook for the entrance test answers, giving them an unfair advantage. After being disqualified and finding out about the fact, Ji-won confronted Chang-wook and he kills her to cover up his misconduct. The sole witness to the incident, Beom, slowly became mad as he felt that Ji-won had been haunting him ever since. Mr. Kim and his wife (the woman who hang Myong-heo) decided to kill Chang-wook and all the students whose parents they deem responsible for their daughter's death.
The film closes with I-na seeing that she tops the class ranking, and it is implied that Beom's attacks was due to her being possessed by Ji-won since the beginning.
- Min Hye-Yeong - drowned in an enclosed glass tank.
- Mr. Lee - beaten to death off screen.
- Sohn Dong-Hyuk - Suffocated with candle wax, then dropped from the ceiling to the gym floor.
- Cha Jae-Wook - killed by blood loss from hundreds of cuts, then his mouth was stuffed with flower petals.
- Yoon Soo-Jin - stuffed into a washing machine, then someone turned it on.
- Kang Hyun - stabbed repeatedly by Beom, the "crazy" student who is haunted by Ji-won's ghost
- Cho Beom (the crazy student)- hit in the head with a rock by Hwang Chang-Wook
- Yoon Myung-Hyo - dropped from the ceiling head-first.
- Kim Ji-Won's Mother - strangled by Hwang Chang-Wook
- Hwang Chang-Wook - stabbed by the father of Kim Ji-Won.
- 1st : Solve all of equations which are written down to a blackboard, and combine them into one complete answer in time. => x^2+y^2-2x+4y+3=0 (Central point coordinate and radius are (-1, -2), 2, respectively), and x^2+y^2-2x+4y-31=0 (Central point coordinate is also (-1, -2) and the radius is 6). There are 2 equations of circle which are given as hints: x^2+y^2-10x+12y+57=0 (Central point coordinate and radius are (5, -6), 2, respectively), and x^2+y^2-10x-4y+25=0 (Central point coordinate is (5, 2), radius is 2 as well). (The circles constructed a picture of a bear which is the same as the shape of the key chain Hwang Chang-Wook was having when he killed Kim Ji-Won)
- 2nd : No. 2 overall ranking sins committed by the student's mother indicated eora of eight characters to Hanja. And then find the answers to show the hanja in the auditorium. => 知足不辱 知止不殆(Hangul: 지족불욕 지지불태). (It means the greed of the parents who get future exam questions from Hwang Chang-Wook)
- 3rd : Kim Ji-Won—previously ranked first on spring—died. Complete the sentence associated with it. => "One fine spring day, remember the auditorium." (Hangul: 따뜻한 봄날의 강당을 기억해.) (It consists of several kinds of anagram, associated with the array of old cell phone keypad.)
- 4th : By doing the puzzle, please complete the sentence. => "I know who killed me. My anger will endure, face the truth." (Hangul: 나는 누가 죽였는지 알고 있다. 나의 분노는 멈추지 않을 것이다. 진실을 대면하라.)
- 5th : Input the number as password by resolving these association with this number sequence. Then, Speak the meaning of the number. You have only one chance. : 5685 -> 2485 -> ? => 1320. To solve, Focus on the inner 2-digit number. Multiply each 1-digit (6 X 8 = 48), and Focus on the outer side numbers (5, 5), and then multiply each 1-digit (5 X 5 = 25), Then the next sequence is 2485. Repeat this once more: 1320. (It means '1st grade, 3rd class and 20th student, Kim Ji-Won')
- 6th : "2 years ago, on one fine spring day, my daughter was murdered by someone with a bear-shaped key chain, who is it? Only the culprit would know the answer. Step forward and confess your sin; if you don't, everyone here will die." => Hwang Chang-Wook, Kang I-Na's Teacher.
Shot on HD video with a budget of ₩1.3 billion, Death Bell is the feature film directorial debut of Chang, a former music video director, who also co-wrote the screenplay with Kim Eun-kyeong. The film also marks the acting debut of Nam Gyu-ri, a former singer with K-pop trio SeeYa, and stars veteran comic actor Lee Beom-soo in his first horror film role.
The only Korean horror film to be released in the summer of 2008, Death Bell made its premiere in July 2008 at the 12th Puchon International Fantastic Film Festival. Post-production on the film had been rushed in order to have it ready for the festival, and director Chang had to apologise for the poor state in which it was shown.
Death Bell was released on DVD on 8 November 2008.
Derek Elley of Variety found Death Bell to have a "neat concept" with "enough shocks and gore to keep genre addicts contented", and commented, "After a fairly conventional half-hour setup, the pic keeps the tension high with tight cutting and a no-flab script that ups the student body count in some especially inventive ways. Solution to the whodunit is less convincing than the lead-up, with a finale that doesn't deliver on expectations. But the journey there is fine, with Lee, better known for comedy, interestingly cast as the students' tough prof." Kyu Hyun Kim of Koreanfilm.org was more critical of the film, saying, "Death Bell annoyingly combines prettified, slick visual filmmaking (but with no real depth) and gag-inducing torture porn excesses: it's simultaneously tepid and lackluster on the one hand and gross and offensive on the other"; he also regarded the screenplay as a "fetid mess" with an unconvincing central premise, but gave credit to the performance of Lee Beom-soo. A review for Twitch also labelled the film's premise as "ridiculous", going on to say, "Lee Beom-Soo certainly tries, and the tempo keeps building decently until the end, but there’s really no vibe to it. It’s just a succession of tortures and murders, with no sense of surprise, no interest... [and] no thematic consciousness whatsoever".
Released on 6 August 2008 in 366 theatres nationwide, the film grossed $2,370,785 and received 575,231 admissions on its opening weekend, placing it third at the local box office. By its third week, Death Bell had climbed to second at the box office, and as of 14 September 2008 had grossed a total of $9,274,859.
Death Bell had looked set to become the second most popular Korean horror film after A Tale of Two Sisters, which attracted more than 3 million viewers in 2003; however, admissions of 1,636,149 (as of 14 September 2008) were less than those recorded by R-Point and Wishing Stairs. Nevertheless, the film attracted more than twice the number of viewers required to break even at the box office.